The Two-Photon Exchange Experiment at DESY

TL;DR

This paper proposes a new experiment at DESY to measure positron-proton and electron-proton scattering ratios, aiming to better understand two-photon exchange effects beyond single-photon interactions in hadronic physics.

Contribution

It introduces a novel high-luminosity measurement setup at DESY to extend the kinematic range of two-photon exchange studies in elastic scattering.

Findings

Higher luminosity than previous experiments

Extended Q^2 range up to 4.6 (GeV/c)^2

Detailed experimental setup and run plan

Abstract

We propose a new measurement of the ratio of positron-proton to electron-proton elastic scattering at DESY. The purpose is to determine the contributions beyond single-photon exchange, which are essential for the Quantum Electrodynamic (QED) description of the most fundamental process in hadronic physics. By utilizing a 20 cm long liquid hydrogen target in conjunction with the extracted beam from the DESY synchrotron, we can achieve an average luminosity of $2.12\times10^{35}$ cm$^{-2}\cdot$s$^{-1}\cdot$sr$^{-1}$ ($\approx200$ times the luminosity achieved by OLYMPUS). The proposed TPEX experiment entails a commissioning run at 2 GeV, followed by measurements at 3 GeV, thereby providing new data up to $Q^2=4.6$ (GeV/$c$)$^2$ (twice the range of current measurements). We present and discuss the proposed experimental setup, run plan, and expectations.